Understanding how B lymphocytes develop and how immunoglobulin is produced is critical for development of effective vaccines and for intervention in immunologic diseases where antibodies are either over-or under-expressed. Appropriate immunoglobulin expression is directly linked to normal B cell development. The transcription factor, Bright (B cell regulator of immunoglobulin heavy chain transcription) enhances immunoglobulin transcription and associates with Bruton's tyrosine kinase (Btk), the defective enzyme in X-linked immunodeficiency disease. Mice and patients with Btk deficiencies exhibit blocks in B cell differentiation that result in abnormally low serum immunoglobulin levels. Data now suggest that Bright activity critically requires Btk function. Therefore, the objectives of this proposal are to determine how Bright activity is regulated and whether it is required for normal B cell development and immunoglobulin production. Transgenic mice producing dominant negative Bright have been produced and will be assessed for appropriate immune responses and development of B cell subpopulations. A third protein has been implicated in Bright function, and it will be further characterized and its contribution to Bright activity and heavy chain transcription will be addressed using conventional reporter assays. In addition, the transcriptional and post-translational regulatory events that result information of active Bright complexes will be identified by direct analysis of the Bright promoter, by identifying signaling intermediates necessary for Bright transcription and by determining the requirements for protein interactions among members of the Bright complex. The results of these experiments will contribute to our understanding of immunoglobulin heavy chain transcription in general, and will provide important insights regarding the relationships between Bright activity, normal B cell development and immunodeficiency disease.